The Federal Regulations of the Food and Drug Administration permit canners of foods to acidify their products to a pH of 4.6 or below as an alternative to thermal retort sterilization. By acidification of such products to a pH of 4.6 or below, the products are rendered microbiologically safe if the products are sealed into containers at elevated temperatures, and held for a sufficient time to destroy molds, yeasts, and vegetative bacteria prior to cooling. Most acidified foods are kept at a pH well below 4.6, because above about 4.2, growth of Bacillus coagulans occurs, causing flat sour spoilage of the product. Acidification permits use of less severe processing conditions without sacrificing product safety.
Several techniques for acidification are used by processors of acidified food. These include (1) blanching of the food ingredients in acidified aqueous solutions; (2) immersion of the blanched food in acidified aqueous solutions; (3) direct batch acidification by adding a known amount of an acid solution to a specified amount of food; (4) direct addition of a predetermined amount of acid to individual containers during production; and (5) addition of acids foods to low-acid foods in controlled proportions to conform to specific formulations.
When meat, poultry, or textured protein is a component of acidified foods it acts as a buffer and raises the pH of the product. At a higher pH the growth of bacteria is favored. In addition, the internal pH of pieces of textured protein, meat, or poultry, can have a center pH greater than that of the food product as a whole, thus providing an environment favoring bacterial growth. Therefore, to insure product safety and stability it must be permitted to equilibrate to assure that a low center pH has been achieved for all discrete food pieces.
U.S. Pat. No. 3,886,296 of Brooks et al., issued May 27, 1975, discloses a hot acid blanching process for canning foods wherein the food particles are blanched with a hot acid solution at a temperature of 71.degree. C. to 100.degree. C. to a pH of 5.0, immediately thereafter submersed totally within a liquid phase having a pH below 4.5, and heat sterilized. The pH of the food particles is decreased to 4.5 usually within 30 minutes after the food particles and liquid phase are combined and sealed in a container. The pH of the food is measured on the total product in comminuted form. However, it has been found that for products containing textured protein, as the pH is decreased, the textured protein begins to acquire a sharp, sour, astringent flavor, presumably due to some chemical change in the material. Thus, acidification can have a detrimental effect on protein flavor. In addition, if ground meat or poultry is acidified to below about 4.8 prior to its combination with a liquid or sauce phase the meat becomes discolored and disintegrated. Acid blanching causes destruction of cellular integrity, and meat or poultry becomes soft or mushy in texture at a pH below about 4.8. Acidification can also have an adverse effect on the texture of protein. Acidification of textured protein can cause it to disintegrate by decreasing the functionality of the binder employed. As pH decreases, binding generally decreases. Texture and flavor of the meat, poultry, or protein pieces is critical to product quality and acceptance. A process for acidification of food products containing significant amounts of textured protein which rigorously protects product safety, while having a minimal impact on product flavor and texture is needed.
U.S. Pat. No. 3,736,148 of Katz, issued May 29, 1973, discloses meat analogs resistant to microbiological spoilage having a pH between 3.0 and 5.4 and a water activity of below 0.95. Katz restricts the water level of the analogs as an aid in preventing the growth of microorganisms. Restriction of water activity limits the optimum texture and flavor which can be achieved. The Katz analogs contain preservatives and texture modifiers such as starches, gums, and the like. Products without food additives such as preservatives and texture modifiers are preferred by consumers. It is desirable to have textured protein products which do not contain preservatives and texture modifiers that are microbiologically safe without restriction of the water activity in order to optimize texture and flavor.
British Pat. No. 1,503,420 discloses a low-temperature protein extrusion process followed by washing with an aqueous solvent. The process yields a textured protein concentrate of meat-like texture by extracting water-soluble constituents from a protein extrudate having a density of 85 to 150 g./l. after drying to less than 8% moisture, using an aqueous solvent at a pH of 5.5 to 6.0 and a temperature above 65.degree. C. However, if the aqueous solvent has a pH of less than 5.5 the product generated is tough, chewy, and too dry, according to Table II on page 6 of the patent.
A process has now been found for acidification of a product containing textured protein. Disintegration of the protein particles is avoided and an optimum texture is provided. No increase in sour flavor occurs despite the decrease in pH. Removal of the acid from the protein minimizes the added anion level in the protein to minimize sour flavor without materially affecting the lowered pH and product safety. Thus, a microbiologically safe product containing textured protein or analog having a desirable texture and acceptable flavor can be generated by this acidification process.
It is therefore an object of this invention to provide a process for the preparation of an acidified protein extrudate, acidified analog, and acidified sauce products containing textured protein without disintegration of the protein.
It is a further object of this invention to provide a process for the preparation of an acidified protein extrudate, acidified analog and acidified sauce products containing textured protein of low pH with an acceptable flavor.
It is a further object of this invention to provide a process which renders a food product having a pH less than 4.6 and containing high levels of textured protein bacteriologically safe and shelf-stable.
It is a further object of this invention to provide an acidified protein extrudate, analog, or sauce product prepared according to the process defined herein.
These and other objects of the invention will become obvious from the following descriptions and examples.